| AVS 59th Annual International Symposium and Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS+EM-MoM |
| Session: | Atmospheric Plasma Processing and Micro Plasmas |
| Presenter: | T. Yagisawa, Keio University, Japan |
| Authors: | T. Yagisawa, Keio University, Japan T. Makabe, Keio University, Japan |
| Correspondent: | Click to Email |
A microcell plasma at atmospheric pressure has been widely investigated. One of the biggest advantages is in the capability to produce a small-size and high-density plasma, broadening a range of applications such as nano-material synthesis, light sources, biomaterial processing, green technology and so on. With decreasing the size of the reactor, the ratio of volume to surface area also decreases. Under these circumstances, the contribution of the wall surface to the loss of charged and neutral particles becomes much larger. The energy is accumulated in the plasma in the form of a thermal energy by the interaction between energetic ions and gas molecules and the ion impact on the wall. Therefore, the effects of local heating of gas molecule on the plasma structure is of great inportance particularlly in a microcell plasma at high pressure.
In this study, the two-dimensional (2D) structure of a capacitively coupled microcell plasma (CCP) driven at radio frequency (13.56 MHz) with the power of ~4.7 W cm-3 is numerically investigated in a sealed cylindricals chamber at atmospheric pressure. Pure argon is considered as a parent gas molecule, where electron, Ar+, Ar2+ and long-lived metastable atom (Arm) are traced in the simulation. In order to discuss the effects of local gas heating, the governing system consisting of a coupled set of models is developed: a neutral transport model including the gas temperature Tg, a conventional plasma model in gas phase, as well as a heat conduction model in solid phase. Large amount of metastable atom ~1014 cm-3 makes huge influence on the plasma structure via stepwise ionization process caused by low energy electrons (~4.3 eV), as well as metastable pooling. The temperature dependence of the thermal conductivity (~ Tg1/2) of argon is considered and the result is compared with that of constant thermal conductivity. The local peak of gas temperature Tg ~ 600 K appears due to the Joule heating by energetic ions in the sheath region in front of the powered electrode, resulting in the local reduction of gas density Ng(r) under the constant gas pressure. Taking the gas heating into account, electron density increases by the enhancement of reduced field E/Ng(r). In addition, electron density distribution slightly expands toward the radial direction.